PARIS—Cities, towns, and villages across France were practically empty on Saturday as residents stayed home and businesses shut to observe a nationwide curfew intended to help stem the spread of coronavirus, especially a more infectious variant. The virus has killed 70,000 people in France, the seventh highest toll in the world, and the government is particularly worried by the more transmissible variant first detected in Britain, which now accounts for about 1 percent of new cases. The curfew was brought forward two hours to 6 p.m. and will run until 6 a.m. In addition, from Monday, anyone travelling to France from outside the European Union will have to show a negative test result and self-isolate for a week upon arrival. “These measures were necessary given the situation. While worsening, it remains relatively better than many countries around us, but I took them because the context, notably with the evolution of …